Schematic of (a) in-plane biaxial

tensile stress and (b) TDs

Glided Plane

Treading Dislocation

a)

b)

1 2 3 4 5 6 7 8 9 time(s) ×10-7

2.5

2

1.5

1

0.5

0

-0.5

-1

-1.5

Am

plit

ud

e (

a.u

.)

Pos Neg Added

×10-3

Diagram for TTG and lab setup.

Excitation Pump ~ (515nm) Probe + Reference ~ (532nm)

The multilayered structure dominates the thermal conductivity, the results

indicate the absence of a substrate effect, and thus, we are effectively

measuring the structure as a bulk semi-infinite material. Lattice constant

mismatch results in residual stress in samples, which results in less efficient

thermal transport.

Expected results for the analysis of TDs, attribute a decrease in thermal

conductivity to an increase in phonon scattering due to a higher threading

dislocation density.

These results indicate the importance of growing GaAs through rational design

of applied residual thermal stress and with a significant reduction of TDD on

device structures, all this to obtain a higher thermal conductivity and improve

heat dissipation.

The significant reduction of the thermal conductivity of GaAs substrates on Si is

detrimental to the heat dissipation capability of photonic devices, reducing the

device lifetime.

0 100 200 300 400 500 600 700 800 900

time (μ s)

No

rma

lize

d A

mp

litu

de

(a

.u.)

TTG Signal Best-fit

1.2

1.0

1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

We analyze different grating periods ranging from 8.0 μm to 18.8 μm. The TTG

time traces were normalized and analyzed using the complete solution to the

thermo-elastic equation, we apply a best-fit with an error function.

We plot results to make a relation between grating period and thermal

diffusivity. Results showed that the obtained values are independent of the

grating period. We observed a decrease on thermal diffusivity when growing on

s-GaP compare to when growing on s-Si. This decrease in diffusivity is

attributed to residual stress present in the GaAs layers in the s-Si samples,

caused by lattice constant mismatch.

Schematic of (a) in-plane

biaxial tensile stress and (b)

TDs

TTG is a technique used where two coherent laser pulses cross at an angle to

make an interference pattern in a sample, producing spatially periodic material

excitations pulses that give rise to thermal expansion.

The relaxation present is attributed to the thermal and acoustic response of the

sample and is monitored through diffraction of a third laser beam. We control

the spatial temperature profile by changing the period of the induced thermal

grating, which in turn changes the thermal penetration depth probed by the

laser.

We measured GaAs films of 3 μm thickness grown on GaP and Si substrates

with estimated in-plane biaxial stress of roughly 250 MPa. For TDDs analysis

We measured three GaAs films of 3 μm thickness grown on Si substrates with

different threading dislocation densities between 3x10⁶ dislocations/cm³ to

3x10⁹ dislocations/cm³ .

In the filed of photonics, it is important to understand the effects of threading

dislocations (TDs) and residual thermal stress on the heat dissipation of gallium

arsenide, as this affects the efficiency of the photonic devices and their lifetime.

Ordered multilayered structures of GaAs have been observed to have

interesting and advantageous properties in fields like photonics and

optoelectronics.

In this work, we execute a noncontact laser-induced transient thermal grating

(TTG) technique to investigate properties like thermal conductivity and

diffusivity of GaAs-based buffers.

Determination of Thermal Properties of GaAs

Thin Film Semiconductor DevicesAlejandro Murillo, Usama Choudhry, Bolin Liao

Department of Mechanical Engineering, University of California Santa Barbara

Introduction

Results

Conclusions

Methods – Transient Thermal Grating (TTG)

GaAs atomic structure and GaAs based buffers.

We must experimentally

corroborate the increase of

residual thermal stress and the

increase of threading dislocation

densities as main factors in the

reduction of the thermal diffusivity.

We add the two obtained

relaxation times to reduce noise

produced by the oscilloscope.

Acknowledgements

Residual thermal stress arise when films are

subjected to a temperature change that results in

thermal expansion and imperfectly coherent

interfaces with their substrates, due to a difference in

the spacing of atoms.

It has been known that TDs can scatter phonons.

When the unit cell of a crystal structure contains

more than one atom, it will contain two types of

phonons, acoustic and optical, with acoustic phonons

being the main heat carrier.

Plotted raw data

Obtained thermal diffusivity values as a

function of the grating period

Thermal diffusivity values for

substrates (First two rows) shown

opposite behavior as literature values

(Third and forth rows).

a)

b)

a) Thermal diffusivity, b) Shear modulus, c) Poisson’s ratio,

d) Density, e)Heat capacity

This research was supported by the LSAMP program of the National Science

Foundation under Award no. HRD- 1826900. A special thank to Dr. Bolin Liao

and mentor Usama Choudhry for welcoming me in their laboratory and advising

me for a successful research project.

0 100 200 300 400 500 600 700 800 900

time (μ s)

No

rma

lize

d A

mp

litu

de

(a

.u.)

TTG Signal Best-fit

1.2

1.0

0.8

0.6

0.4

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0

-0.2

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-0.6

a)

0 200 400 600 800 1000 1200 1400

time (μ s)

No

rma

lize

d A

mp

litu

de

(a

.u.)

TTG Signal Best-fit

1.4

1.2

1.0

1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

0 100 200 300 400 500 600 700 800 900

time (μ s)

No

rma

lize

d A

mp

litu

de

(a

.u.)

TTG Signal Best-fit

1.2

1.0

1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

Sample analysis for grating periods (a) 8.0 μm and (b) 18.8 μm

0 100 200 300 400 500 600 700 800 900

time (μ s)

No

rma

lize

d A

mp

litu

de

(a

.u.)

TTG Signal Best-fit

1.2

1.0

1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

b)

3 μm GaAs

GaAs, GaP, Si